Employee Benefits, LTIP and UAR and Cash Bonus Plan (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
LTIP and UAR and Cash Bonus Plan
Deferred Compensation and Share-based Compensation, Expense	$ 1.4	$ 6.2

Compensation expense recognized during the period pertaining to the deferred compensation arrangement and the share-based compensation arrangement.

No definition available.

Name:	bwp_DeferredCompensationAndShareBasedCompensationExpense
Namespace Prefix:	bwp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration